Chasing obscuration in type-I AGN: discovery of an eclipsing clumpy wind at the outer broad-line region of NGC 3783

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: M.Mehdipour@sron.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
⁵ Department of Physics, Technion-Israel Institute of Technology, 32000 Haifa, Israel
⁶ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁷ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
⁸ INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁹ European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁰ Department of Astronomy, University of Geneva, 16 Ch. d’Ecogia, 1290 Versoix, Switzerland
¹¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
¹² Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
¹³ Center for Cosmology & AstroParticle Physics, The Ohio State University, 191 West Woodruff Ave., Columbus, OH 43210, USA
¹⁴ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
¹⁵ CNRS, IPAG, 38000 Grenoble, France
¹⁶ Institute of Astronomy, Madingley Road, CB3 0 HA Cambridge, UK
¹⁷ Max Planck Institute fur Extraterrestriche Physik, 85748 Garching, Germany

Received: 15 May 2017
Accepted: 12 July 2017

Abstract

In 2016 we carried out a Swift monitoring programme to track the X-ray hardness variability of eight type-I AGN over a year. The purpose of this monitoring was to find intense obscuration events in AGN, and thereby study them by triggering joint XMM-Newton, NuSTAR, and HST observations. We successfully accomplished this for NGC 3783 in December 2016. We found heavy X-ray absorption produced by an obscuring outflow in this AGN. As a result of this obscuration, interesting absorption features appear in the UV and X-ray spectra, which are not present in the previous epochs. Namely, the obscuration produces broad and blue-shifted UV absorption lines of Lyα, C iv, and N v, together with a new high-ionisation component producing Fe xxv and Fe xxvi absorption lines. In soft X-rays, only narrow emission lines stand out above the diminished continuum as they are not absorbed by the obscurer. Our analysis shows that the obscurer partially covers the central source with a column density of few 10²³ cm^-2, outflowing with a velocity of few thousand km s^-1. The obscuration in NGC 3783 is variable and lasts for about a month. Unlike the commonly seen warm-absorber winds at pc-scale distances from the black hole, the eclipsing wind in NGC 3783 is located at about 10 light days. Our results suggest that the obscuration is produced by an inhomogeneous and clumpy medium, consistent with clouds in the base of a radiatively driven disk wind at the outer broad-line region of the AGN.